After decades of oil production, the oil reservoirs with rich reserves and low difficulty in drilling exploitation have been basically run out. Domestic and international oil drilling has evolved from shallow surface to deep strata, and from the shallow bay to the deep sea. In china, taking Tarim Oilfield as an example, the drilling depth of Ha 7-11H well is 7341.25 meters, the vertical depth is 6645.83 meters, the horizontal displacement is nearly 800 meters, the maximum inclination is 90 degrees and the highest downhole temperature is 168 degrees Celsius, thus creating a new horizontal well drilling record in china. The CNOOC deepwater semi-submersible drilling platform has a maximum operating depth of 3,000 meters, and a maximum drilling depth of 12,000 meters. Internationally the maximum drilling depth is up to 15,000 meters. As the drilling depth increases, the requirements for the performance of oil drilling steel continue to increase. The steel for oil drilling can be divided into magnetic steel and non-magnetic steel according to the magnetic functions. Non-magnetic steel is mainly used as a sensor protection device. Typical application is used in non-magnetic drill collar, to exert bit pressure to the drills, reduce the vibration of the drill bit to make drill bit to operate stably while monitoring the drilling process.
The non-magnetic drill collar must be of fully austenite structure, with excellent hardness, toughness, impact value and corrosion resistance, and low permeability and excellent machinability. At present, the commonly used non-magnetic steel is mainly 200 and 300 series steels. However, for the 200 and 300 series steels, after treatment with conventional methods, their strength and hardness can only reach 50% of the requirements for oil drill collar while ensuring the fully austenite structure. When the 200 and 300 series of steels are subject to conventional cold-working reinforcement, their strength and hardness can be significantly improved, but their ductility and toughness are seriously damaged, and partial or whole austenite is converted to martensite structure, producing strong magnetism. Therefore, the currently used austenitic stainless steel and processing methods are difficult to meet the rigorous requirements for steels with the continuous increase in the drilling depth.